With a machine tool such as a numerically controlled lathe or a machining center, a spindle is rotated to move a tool rest, a spindle head and the like in order to perform cutting work on a work piece. Thus, the temperature of the respective components of the machine tool will rise due to the heat generation in the motor or rotating portion and the heat generation caused by the contact of the tool and the work piece.
Even in the following morning after the operation of the machine tool is ended, there are cases where the heat generated in the previous day remains in the respective components of the machine tool. Consequently, thermal displacement caused by the temperature difference between the temperature in the room in which the machine tool is installed and the temperature in the working area will occur in the respective components of the machine tool, which is undesirable in terms of working accuracy.
With the working machines disclosed in Japanese Patent Application Laid-open No. 2003-291050: Patent Document 1 and Japanese Patent Application Laid-open No. 2006-102939: Patent Document 2, the temperature in the working area is controlled to be a predetermined temperature and the working accuracy is prevented from being lowered due to thermal displacement by covering the entire working machine with a cover and supplying cool air, the temperature of which is controlled with an air conditioning unit using a cooling medium such as fluorocarbon (CFC), inside of the cover.
Nevertheless, since the working machines disclosed in Patent Document 1 and Patent Document 2 require an air conditioning unit, they are expensive and much energy must be spent in order to control the temperature in the working area to be a predetermined temperature.